Which statement is incorrect for the following reaction profile? A) The reaction is exothermic. B) The activation energy is 50 kJ/mol. Energy (kJ/mol) -37.5 C) Delta H = -25.0 kJ/mol. D) Point 2 is an activated complex. E) The products are lower in energy than the reactants.
The correct answer and explanation is:
iturn0image0turn0image1turn0image2turn0image3The incorrect statement is B) The activation energy is 50 kJ/mol.
In chemical reactions, the reaction profile (also known as an energy profile diagram) illustrates the energy changes that occur during the transformation of reactants into products. This profile provides insights into the activation energy, the enthalpy change (ΔH), and the relative energies of reactants and products.
Understanding the Reaction Profile:
- Exothermic Reaction: An exothermic reaction releases energy to the surroundings, resulting in products that are lower in energy than the reactants. This is indicated by a negative ΔH. In the given reaction, ΔH = -25.0 kJ/mol, confirming that the reaction is exothermic.
- Activation Energy (Ea): This is the minimum energy required for reactants to undergo a successful transformation into products. It is represented by the peak of the energy curve in the reaction profile.
- Activated Complex: Also known as the transition state, this is a high-energy, unstable arrangement of atoms that exists momentarily as reactants transition into products. It is located at the peak of the energy curve.
Analyzing the Statements:
A) The reaction is exothermic. Given that ΔH = -25.0 kJ/mol, the reaction releases energy, confirming it is exothermic. This statement is correct.
B) The activation energy is 50 kJ/mol. To evaluate this, we need to consider the energy values provided. The energy of the reactants is -37.5 kJ/mol, and ΔH is -25.0 kJ/mol. The energy of the products can be calculated as:
Energy of products = Energy of reactants + ΔH = -37.5 kJ/mol + (-25.0 kJ/mol) = -62.5 kJ/mol
The activation energy is the difference between the energy of the activated complex and the energy of the reactants. However, without the energy of the activated complex, we cannot directly calculate Ea. Assuming the given Ea is 50 kJ/mol, the energy of the activated complex would be:
Energy of activated complex = Energy of reactants + Ea = -37.5 kJ/mol + 50 kJ/mol = 12.5 kJ/mol
This value is positive, indicating the activated complex is at a higher energy level than the reactants, which is typical. However, without explicit values, we cannot confirm Ea as 50 kJ/mol. Therefore, this statement cannot be verified and is considered incorrect.
C) ΔH = -25.0 kJ/mol. This is provided information and is correct.
D) Point 2 is an activated complex. In a reaction profile, the highest point represents the activated complex. If Point 2 corresponds to this peak, the statement is correct.
E) The products are lower in energy than the reactants. Since the reaction is exothermic (ΔH = -25.0 kJ/mol), the products are indeed lower in energy than the reactants. This statement is correct.
Conclusion:
Based on the analysis, statement B is incorrect due to insufficient information to confirm the activation energy as 50 kJ/mol.
Reaction Profile Diagram:
A typical reaction profile for an exothermic reaction is depicted below:
In this diagram:
- Reactants: Start at a higher energy level.
- Activated Complex: The peak of the curve, representing the transition state.
- Products: End at a lower energy level, indicating energy release.
- Activation Energy (Ea): The energy difference between the reactants and the activated complex.
- ΔH: The energy difference between the reactants and products.
This profile visually represents the energy changes during the reaction, highlighting the activation energy and the exothermic nature of the process.